Linux Slob分配器(三)--释放对象

水平有限，描述不当之处还请指出，转载请注明出处http://blog.csdn.net/vanbreaker/article/details/7705792

slob释放对象由函数slob_free()来完成，分为三种情况进行处理：

slob中已有的空闲单元加上释放对象块的空闲单元正好等于一个空闲的page，那么将直接将该page释放回伙伴系统slob中已无空闲单元，那么这次释放将更新slob的信息普通情况，即slob处于部分满状态，那么更新slob的信息的同时还要将释放的块插入到相应的位置，要注意插入后是否能和相邻块进行合并！

下面来看具体的代码

/* * slob_free: entry point into the slob allocator. */static void slob_free(void *block, int size){struct slob_page *sp;slob_t *prev, *next, *b = (slob_t *)block;slobidx_t units;unsigned long flags;if (unlikely(ZERO_OR_NULL_PTR(block)))return;BUG_ON(!size);sp = slob_page(block);//获取slob地址units = SLOB_UNITS(size);//计算释放的单元数spin_lock_irqsave(&slob_lock, flags);/*slob剩余的单元数加上待释放的单元数正好等于一个slob本有的总单元数， 直接将slob占用的页框释放回伙伴系统*/if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {/* Go directly to page allocator. Do not pass slob allocator */if (slob_page_free(sp))clear_slob_page_free(sp);spin_unlock_irqrestore(&slob_lock, flags);clear_slob_page(sp);free_slob_page(sp);slob_free_pages(b, 0);return;}if (!slob_page_free(sp)) {//slob没有空闲块/* This slob page is about to become partially free. Easy! */sp->units = units;//设置slob的单元数为释放对象的单元数sp->free = b;//设置首对象为释放对象set_slob(b, units,//最后一个对象的空闲对象设置为下一个页的首个单元(void *)((unsigned long)(b +SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));set_slob_page_free(sp, &free_slob_small);//将slob链入free_slob_small链表goto out;}/* * Otherwise the page is already partially free, so find reinsertion * point. */sp->units += units;//空闲单元总数增加unitsif (b < sp->free) {//待释放块的地址小于sp->freeif (b + units == sp->free) {//可以合并units += slob_units(sp->free);sp->free = slob_next(sp->free);//取free的下一个空闲对象作为free}/*将释放块插入在free前面，并将其作为首个空闲块赋给free*/set_slob(b, units, sp->free);sp->free = b;} else {prev = sp->free;//取首个空闲块next = slob_next(prev);//取第二个空闲块while (b > next) {//扫描至待释放块处prev = next;next = slob_next(prev);}/*将b插在prev和next中间，prev-->b-->next,要考虑是否能够合并*/ /*如果prev不是最后一个空闲块并且b可以和next合并，则进行合并*/if (!slob_last(prev) && b + units == next) {units += slob_units(next);set_slob(b, units, slob_next(next));} else//否则将b插入在next前面set_slob(b, units, next);if (prev + slob_units(prev) == b) {//如果prev可以和b合并，则进行合并units = slob_units(b) + slob_units(prev);set_slob(prev, units, slob_next(b));} else//否则，将b插在prev后面set_slob(prev, slob_units(prev), b);}out:spin_unlock_irqrestore(&slob_lock, flags);}

1楼zi77642475前天 10:04

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